This invention relates to a method of making certain relatively reactive organometallic complex compounds using reverse osmosis.
Organometallic complex compounds have frequently found utility in catalyst systems. In many instances the catalysts operate by the formation of weak complexes with one or more reactants. It is frequently found that the catalytic species is a ligand-deficient species, or a species containing one or more ligands which are readily displaced by a reactant molecule. Such species are often highly reactive and cannot be isolated by direct chemical methods.
The present invention is therefore directed to a process of producing reactive organometallic complexes by reverse osmosis techniques.
Reverse osmosis is a well known technique which has been employed in a wide variety of applications. Thus U.S. Pat. No. 3,567,632 to J. W. Richter and H. H. Hoehn teaches the preparation of permselective membranes and their use in the desalination of water. Reverse osmosis has been used to separate complexes from a homogeneous fluid mixture using polyolefin membranes (Netherlands Pat. No. 70/08849 to British Petroleum). Similar disclosures teaching the use of cellulosic and of silicone membranes are found in British Pat. Nos. 1,243,507 and 1,243,508 respectively.
The variables in these processes are so chosen as to decrease the concentration of the transition metal complex in the permeate. The examples show separation of the rhodium complex Rh(Bu.sub.3 P)CO (acetylacetonate), from toluene or heptaldehyde solvents, the latter having been formed by the rhodium complex-catalyzed hydroformylation of hexene. The catalyst solution, now at increased concentration, is recycled.
British Pat. No. 1,212,758 teaches that poly(vinyl pyrrolidone) is separated into fractions of differing molecular weight by contacting a solution of the poly(vinyl pyrrolidone) with the upstream side of a fluid permeable microporous anisotropic membrane under a pressure greater than the pressure on the second, downstream side, thereby forcing a portion of the poly(vinyl pyrrolidone) through the membrane. Among the suitable membrane materials for this process are included polyamides and polyimides.